1. Field of the Invention
The invention relates generally to systems and methods for use in the treatment of congestive heart failure and, more particularly, to systems and methods for detecting adventitious lung sounds indicative of lung congestion.
2. Description of the Related Art
Cardiac pacemakers generally provide functions including sensing electrical signals generated by the heart, controlling stimulation of excitable tissues in the heart, sensing the response of the heart to such stimulation, and responding to inadequate or inappropriate stimulus or response, e.g., dysrhythmia, to deliver therapeutic stimuli to the heart. Some existing cardiac pacemakers also function to communicate with an external programmer device to support a variety of monitoring, diagnostic and configuration functions.
Certain cardiac pacemakers include an internal accelerometer for measuring the level of activity of the patient, e.g., movement caused by walking around. Such pacemakers process the accelerometer signals to reduce noise interfering with the measurement of the patient's activity, such as the sounds generated by the heart itself, and then use the processed signals as inputs to algorithms for generating the signals used to control the stimulation of the heart. For example, if accelerometer signals indicate that a patient is walking briskly, the pacemaker may stimulate the heart to beat at a faster rate, often subject to an upper rate limit, than when the patient is at rest.
Cardiac resynchronization therapy (CRT) is a relatively new but promising therapy for the treatment of congestive heart failure (CHF). In CRT, a cardiac pacemaker is implanted to restore synchrony to the beating of the heart, thereby increasing the heart's pumping efficiency.
CHF patients represent a large and growing population of patients that can benefit from implantable devices. CHF as a disease comprises a remarkably complicated set of interrelated systemic dysfunctions involving the cardiac and circulatory systems, the autonomic system, renal system, and the respiratory system. Due to the complex nature of CHF, in order to understand and track the progression of the disease, it is necessary to monitor a variety of symptoms presented by the affected systems.
One of the challenges of managing patients with CHF is to keep their lung congestion under control by adjusting the dosage of their diuretic medications. A sign of lung congestion at patient follow-up is the presence of adventitious lung sounds such as rales or crackles. Rales is an obvious crackling sound present upon auscultation of the chest. The presence of rales likely indicates the need to adjust the patient's diuretic regimen due to increased lung congestion. The worsening of lung congestion may in turn signify deterioration in the patient's underlying cardiac condition. In emergent CHF, the presence of rales is an independent indicator of mortality (Cowie, M. R. et al., “Survival of Patients with a New Diagnosis of Heart Failure: A Population Based Study,” Heart 2000; 83:505:510).
Between follow up visits, the physician has no means of monitoring lung congestion other than relying on the patient to report relevant symptoms. Reliability of patient self-reporting of symptoms may vary considerably from patient to patient, with some patients either becoming unknowingly acclimated to the symptoms, or not wanting to bother their doctor by complaining about their symptoms.
Hence, those skilled in the art have recognized a need for an apparatus and method for monitoring a patient's pulmonary system for the presence of adventitious lung sounds, e.g., rales, indicative of lung congestion. The invention fulfills these needs and others.